Internodal potassium currents can generate ectopic impulses in mammalian myelinated axons.

Positive clinical symptoms can arise from ectopic action potentials in several disorders of myelinated axons. Here we report that an elevated K+ concentration in the periaxonal, internodal space can cause internodal K+ currents to become excitatory, resulting in slow potential oscillations and associated bursts of ectopic spikes. Ectopic firing may therefore be favoured by conditions in which periaxonal K+ buffering is compromised.